1. Field of the Invention
The present invention relates to a control device capable of removing a charge on a magnetic disk when a magnetic disk unit, which includes a loading/unloading mechanism that keeps a magnetic head and a magnetic disk from coming into contact with each other when a power supply is turned off, is in operation, and to a magnetic disk unit including the control device.
2. Description of the Related Art
Conventionally, storage of data in a computer is achieved by a main memory that is a memory unit realized with a semiconductor device. Unless power is supplied, information stored in the main memory disappears. Data is therefore preserved in an external storage device. A magnetic disk unit is often adopted as the external storage device. As the magnetic disk unit, a hard disk drive, including at least one data storage disk coated with a magnetic substance and a magnetic head with which data is read or written on or from the disk, has become the mainstream device because of its large storage capacity. Each disk has a laminated structure having an aluminum or a glass disk base, which is coated with the magnetic substance. The disk is rotated at high speed, using a motor, so that the magnetic head can read or write data.
A hard disk drive can be a hard disk drive of a contact start/stop (CSS) type and a hard disk drive of a loading/unloading type. In the CSS type, when a magnetic disk is halted, a magnetic head is in contact with the magnetic disk. When the magnetic disk is rotated, the magnetic head floats above the magnetic disk. When the rotation of the magnetic disk is ceased, the magnetic head comes into contact with the magnetic disk. In the CSS type, the magnetic head lands in an internal circumferential zone (CSS zone) other than a zone on the magnetic disk in which the data is written. A head slider bearing the magnetic head has projections to prevent, when the magnetic head lands on the magnetic disk, the entire surface of the slider coming into contact with, and being adsorbed by the disk.
As far as the CSS type is concerned, when the power supply of the magnetic disk unit is turned off, the magnetic head or head slider comes into contact with the magnetic disk in the CSS zone. Consequently, a charge on the magnetic disk flows into the base of the magnetic disk unit via the magnetic head or head slider and a head suspension, and is thus removed. Therefore, in the CSS type, after the power supply of the magnetic disk unit is turned off, a charge will not accumulate on the magnetic disk.
On the other hand, the loading/unloading type is such that, when a magnetic disk is halted, a magnetic head is fully separated (unloaded) from the magnetic disk, and held in a holder located outside an outermost circumferential recording zone on the magnetic disk. When the magnetic disk is rotated, the magnetic head is returned to (loaded onto) the magnetic disk. Japanese Unexamined Patent Publication No. 3-232169 describes a hard disk drive of the loading/unloading type that removes foreign matter, which adheres to the magnetic head, during the use of the hard disk drive.
In the magnetic disk unit of the loading/unloading type, once the magnetic disk unit is started, and even when the power supply is turned off, the magnetic disk (medium) and magnetic head do not come into contact with each other. Therefore, a charge on the magnetic disk cannot escape. As the amount of charge increases, the superficial potential of the magnetic disk rises. This poses a problem in that a giant magneto-resistive (GMR) or magneto-resistive (MR) element included in the magnetic head may be broken due to static electricity.